hi matttcattt,
I saw in some other thread a calculation of the power from a chip. From what I remember it is P=V*V/R, being V the voltage swing and R the resistance. If you have 25 V supply, and if the chip can swing up to -4V from the supply, that is 21 V, and if R=8, then the power will be 21*21/8=55W. That´s 2.6 amps, so within the OPA541 ratings.
I have a GC based on the OPA541. I mounted the two channels in a L shaped aluminium bar 20 cm long and 5 cm width (20x5x5 cm). I never play it at the highest volumes but even at a loud volume the aluminium bar does not even get warm.
Miguel
I saw in some other thread a calculation of the power from a chip. From what I remember it is P=V*V/R, being V the voltage swing and R the resistance. If you have 25 V supply, and if the chip can swing up to -4V from the supply, that is 21 V, and if R=8, then the power will be 21*21/8=55W. That´s 2.6 amps, so within the OPA541 ratings.
I have a GC based on the OPA541. I mounted the two channels in a L shaped aluminium bar 20 cm long and 5 cm width (20x5x5 cm). I never play it at the highest volumes but even at a loud volume the aluminium bar does not even get warm.
Miguel
The chip will dissipate the difference between the supply rails and the output voltage, multiplied by the ouput current.
If the supply is +/-18v and the output swing is +/-12v then there's 6v across the device, since only one of the push-pull transistors is on. A load of 8R means the current is 1.5A so the output power is 18W and the dissipation is 9W.
Nice one,
David.
If the supply is +/-18v and the output swing is +/-12v then there's 6v across the device, since only one of the push-pull transistors is on. A load of 8R means the current is 1.5A so the output power is 18W and the dissipation is 9W.
Nice one,
David.
The output swing depends on how loud you set the volume control! Your maximum power will be the supply rails minus a few volts - the actual amount is spec'ed in the data sheet (see OUTPUT section in the table on page two). If you're driving 2A, the swing will typically be the supply rails minus 3.6v.
The output current roughly is the output volatge swing divided by your load impedance.
So, if the supplies are +/-20v, your maximum output swing will be roughly 16.4v. This will give a current of 2.05A into 8R.
Power output is V^2/R = (16.4 x 16.4)/8 = 33.62W
Power dissipated in the chip is V*I = (20 - 16.4)*2.05 = 7.38W
These figures are the maximum you can acheive with a 20v supply and 8R load. You need to recalculate depending on your own situation.
Nice one,
David.
The output current roughly is the output volatge swing divided by your load impedance.
So, if the supplies are +/-20v, your maximum output swing will be roughly 16.4v. This will give a current of 2.05A into 8R.
Power output is V^2/R = (16.4 x 16.4)/8 = 33.62W
Power dissipated in the chip is V*I = (20 - 16.4)*2.05 = 7.38W
These figures are the maximum you can acheive with a 20v supply and 8R load. You need to recalculate depending on your own situation.
Nice one,
David.
It works out as half through the maths although the correct way to calculate is to multiply the swing by 0.707 (the reciprocal of the square root of 2).
If the supplies are +/-20v, your peak output swing will be 16.4v whereas the RMS will be 16.4 * 0.707 = 12.6v. This will result in an RMS current of 1.45A into 8R, giving 16.82W RMS output power.
Nice one,
David.
If the supplies are +/-20v, your peak output swing will be 16.4v whereas the RMS will be 16.4 * 0.707 = 12.6v. This will result in an RMS current of 1.45A into 8R, giving 16.82W RMS output power.
Nice one,
David.
You take the Peak Voltage and multiply time .707 ( square root of 2 divided by 2). Square the result and divide by the load resistance. So your 31 Volt peak output is 21.9 Vrms. Squared is 480.35 and divided by 8 is 60.04. BTW it's hard to get accurate to 3 digits.
If you're measuring the Peak to Peak Voltage you will need to divide by 2 to get to the peak Voltage or else you'll get an answer 4 times larger than it should be.
It gets a little more interesting as the power supply varies with the power output which is why power is specified with continuous sine wave drive. ALSO, the power varies when the line Voltage changes as well. If you measure power with 117 Volt line an the line goes up to 125, a ratio of 1.068 %, the power can go up 1.068 SQUARED or 1.14.
This must be done with a scope to stay out of clipping.
G²
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